This mentored patient-oriented research career development award (K23) will support Dr. Kelly Doran's training and research on the interrelated problems of substance use and homelessness. More than 1.5 million Americans experience homelessness each year. Alcohol and drug use are both risk factors for homelessness, and the problems of substance use and homelessness can each exacerbate the other. Both substance use and homelessness are associated with poor health outcomes, including increased morbidity and mortality, and frequent use of expensive health care services. Homelessness policy in the U.S. is increasingly focused on prevention, yet ideal methods for targeting prevention interventions to at-risk people have been sparsely researched. Furthermore, prevention interventions only reach a small and self-selected subset of people. As the safety net of the health care system, emergency departments (EDs) serve large numbers of patients with unhealthy alcohol or drug use who are at risk for homelessness and may not access services elsewhere. The overall goal of the proposed research is to identify optimal approaches to risk screening and prevention of homelessness in ED patients with unhealthy alcohol or drug use. The specific research aims are: 1) to develop a brief screening tool that will identify ED patients with unhealthy alcohol or drug use who are at significant risk for future homelessness, 2) to use in-depth, qualitative interviews to inform the development of an intervention to prevent homelessness among ED patients with unhealthy alcohol or drug use, and 3) to conduct a feasibility study of an ED-based intervention to prevent homelessness among patients with unhealthy alcohol or drug use. The results of this research will inform a future R-series application to conduct a trial of homelessness prevention and substance use interventions among unhealthy alcohol or drug using ED patients at risk for homelessness. Dr. Doran will be mentored by a transdisciplinary team of experts in health services research, qualitative and mixed methods, prevention and intervention science, substance abuse, and homelessness. The proposed research and training will be conducted at Bellevue Hospital Center, the oldest public safety net hospital in the United States, and at New York University, whose School of Medicine and multiple other professional schools boast unparalleled opportunities for collaborative work and learning. Dr. Doran's training goals for this career development award are to develop and enhance skills in: 1) survey design and psychometric theory, 2) advanced health services research methods, 3) advanced qualitative and mixed methods, 4) intervention and prevention science, and 5) substance abuse, addiction, and homelessness. The proposed research and training plans will provide a strong foundation for Dr. Doran's career as an independently funded clinical investigator dedicated to the interconnected problems of substance use and homelessness.